This invention relates to the production of alloys, and, more particularly, to the preparation and heat treatment of alloys of the gamma titanium aluminide type.
Titanium aluminides are a class of alloys whose compositions include at least titanium and aluminum, and typically some additional alloying elements such as chromium, niobium, vanadium, tantalum, manganese, and boron. The gamma titanium aluminides are based on the gamma phase found at nearly the equiatomic composition, with roughly 50 atomic percent each of titanium and aluminum, or slightly reduced amounts to permit the use of other alloying elements. The titanium aluminides, and particularly the gamma titanium aluminides, have the advantages of low density, good low and intermediate temperature strength and cyclic deformation resistance, and good environmental resistance.
Gamma titanium aluminides have application in aircraft engines. They can potentially be used in applications such as low-pressure turbine blades and vanes, bearing supports, compressor casings, high pressure and low pressure hangars, frames, and low pressure turbine brush seal supports.
One area of continuing concern in the titanium aluminides, and particularly the gamma titanium aluminides, is their low-to-moderate levels of ductility. Ductility is the measure of how far a material can elongate before it fails, and is linked to other properties such as fracture resistance. The gamma titanium aluminides elongate only 1-4 percent at most prior to failure, and have a steeply rising stress-strain curve. Maintaining the strength and resistance of the material to premature failure are therefore highly dependent upon controlling the alloy ductility.
In this context of low-to-moderate ductilities, a key consideration is the ability to achieve and maintain some known minimum ductility. The development of specifications for the use of the material normally start with some minimum property that can be reached on a consistent basis, and then a safety factor is applied. Consistency and controllability become important considerations, and are not easily achieved due to the relatively low ductilities experienced in these materials.
There is therefore a need for an approach to achieving a minimum set of tensile properties, including as high a consistent elongation to failure as possible, in gamma titanium aluminide alloys. The approach must permit those properties to be achieved consistently and controllably in the alloys of interest. The present invention fulfills this need, and further provides related advantages.